Abstract

This experiment involved a survey of damping - off and root rot disease of watermelon in Anbar , Baghdad and Babylon provinces. Determination of pathogens and testing their pathogenesity were also investigated. Results of the field survey showed the existence of the disease in all the surveyed provinces with 13%-27% root rot and post emergence damping off disease and decrease the percentage of germination to 40%-57% in all the surveyed regions. Results of isolation and identification showed the presence of 12 genera and 10 species associated with the infected seedlings. The fungus Fusarium solani was found to be present in all surveyed areas in mean percentage of occurrence of 27.03%. The, F. oxysporum , Phoma spp., Rhizoctonia solani and Cylindrocarpon spp. waer found to be present in percentage of 7.1%, 11.2%, 14.0% and 16.6% respectively. Results of pathogenicity tests of some fungal isolates which were associated with watermelon roots showed that the isolates gave a significant reduction in percentage of seeds germination of watermelon and increased the percentage of disease severity , R. solani isolate (O) had the maximum effect where the germination percent was 6.6% and the disease severity was 93% followed by F. oxysporum isolate (B) where the percentage of seeds germination and disease severity were 10% and 90% respectively , ther isolates showed variable significant reduction in percentage of seeds germination of watermelon ranging betwee 16.6% - 50%. The isolates also increased the percentage of disease severity which were ranging between 50% - 83.3% compared with control treatment in which the germination percentage and disease severity were 90% and 0.0% respectively. Results of the interaction between some of pathogenic fungi isolates showed a reduction in percentage of seeds germination and increase in disease severity . The combination between R. solani (O) isolate + F. oxysporum (B) isolate and R. solani (O) isolate + F. oxysporum (B) isolates + Cylindocarpon sp. The (A) isolate reduced percentage of seeds germination to zero and increased disease severity to 100%. Other combination O+A and B+A reduced percentage of seed germination to 3.3% and 6.6% respectively and increased the disease severity to 96.6% and 93%, respectively.